Systems and methods for forming layers that contain niobium and/or tantalum

ABSTRACT

A method of forming (and system for forming) layers, such as calcium, barium, strontium, and/or magnesium, tantalates and/or niobates, and optionally titanates, on a substrate by employing a vapor deposition method, particularly a multi-cycle atomic layer deposition process.

This application hereby incorporates by reference all of the followingin their entireties: application Ser. No. 10/828,686, filed Apr. 21,2004, now U.S. Pat. No. 7,115,166, which is a continuation ofapplication Ser. No. 10/230,131, filed Aug. 28, 2002, now U.S. Pat. No.6,730,164.

FIELD OF THE INVENTION

This invention relates to methods of forming a layer on a substrateusing a vapor deposition process, particularly a multi-cycle atomiclayer deposition (ALD) process, using one or more Group IIA metalprecursor compounds, one or more Group VB metal (e.g., tantalum and/orniobium) precursor compounds, and optionally other metal (e.g.,titanium) precursor compounds, typically in the presence of one or morereaction gases. The precursor compounds and methods are suitable forexample, for the formation of dielectric layers such as calcium, barium,strontium, and/or magnesium, tantalates and/or niobates, and optionallytitanates, on semiconductor substrates or substrate assemblies.

BACKGROUND

Capacitors are the basic energy storage devices in random access memorydevices, such as dynamic random access memory (DRAM) devices andferroelectric memory (FERAM) devices. They consist of two conductors,such as parallel metal or polysilicon plates, which act as theelectrodes (i.e., the storage node electrode and the cell platecapacitor electrode), insulated from each other by a dielectricmaterial.

The continuous shrinkage of microelectronic devices such as capacitorsover the years has led to a situation where the materials traditionallyused in integrated circuit technology are approaching their performancelimits. Silicon (i.e., doped polysilicon) has generally been thesubstrate of choice, and silicon dioxide (SiO₂) has frequently been usedas the dielectric material to construct microelectronic devices.However, when the SiO₂ layer is thinned to 1 nm (i.e., a thickness ofonly 4 or 5 molecules), as is desired in the newest microelectronicdevices, the layer no longer effectively performs as an insulator due tothe tunneling current running through it. This SiO₂ thin layerdeficiency has lead to the search for improved dielectric materials.

High quality dielectric layers containing Group IIA metal titanates suchas SrTiO₃, BaTiO₃, and (Ba_(1-x)Sr_(x))TiO₃ are of interest to thesemiconductor industry as they exhibit higher permitivities than dodielectric layers containing SiO₂. Consequently, the semiconductorindustry has been extensively evaluating strontium, barium, and titaniumprecursor compounds that can be used in vapor deposition processes.

Chemical vapor deposition (CVD) is a continuous, single step vapordeposition process that can be used to deposit dielectric films (i.e.,layers) having excellent conformality and is therefore of significantinterest in making strontium and barium titanate thin films. In CVD,excellent conformality is achieved when the process is carried out at atemperature low enough that the surface reactions are the rate-limitingstep in the film growth. At higher temperatures the precursor compoundtransformation becomes the limiting factor, causing a degradation of theconformality.

Atomic layer deposition (ALD) is a more sophisticated vapor depositionprocess capable of forming even higher quality dielectric layers due tothe self-limiting film growth and the optimum control of atomic-levelthickness and film uniformity. Using the ALD process, several sequentialprocess cycles are employed to deposit the layer on the substrate onemonolayer at a time per cycle until the desired layer thickness isachieved. For each cycle of the ALD process, vapors of one or moreprecursor compounds are pulsed into the deposition chamber and arechemisorbed onto the substrate. Typically, one or more vaporizedreaction gases (e.g., water vapor) are pulsed into the depositionchamber to react with the chemisorbed precursor compound(s) and causethe deposition of the desired layer onto the substrate. With the ALDprocess, more reactive precursors can be used, without the problem ofgas-phase reactions, resulting in lower temperature requirements at thesubstrate.

Vehkamäki et al., “Growth of SrTiO₃ and BaTiO₃ Thin Films by AtomicLayer Deposition,” Electrochemical and Solid-State Letters,2(10):504-506 (1999) describe thin films of SrTiO₃ and BaTiO₃ depositedby ALD processes making use of a novel class of strontium and bariumprecursors, i.e., their cyclopentadienyl compounds, together withtitanium tetraisopropoxide and water. Prior to their discovery,Vehkamäki et al. state that the selection of strontium and bariumprecursor compounds has been limited to their β-diketonate compoundsthat do not react with water or oxygen at temperatures low enough forthe self-limiting growth mechanism of ALD processes.

The search continues for sufficiently volatile Group IIA metal precursorcompounds, especially strontium and/or barium precursor compounds, toemploy successfully in vapor deposition processes, particularly ALDprocesses, to form dilectric layers, for example.

SUMMARY

This invention provides vapor deposition processes, and particularly amulti-cycle atomic layer deposition (ALD) processes, for forming ametal-containing layer on a substrate using one or more Group IIA metaldiorganoamide precursor compounds, one or more Group VB metal precursorcompounds, and optionally one or more other metal-containing precursorcompounds (e.g., titanium precursor compounds) and/or one or morereaction gases, such as water vapor. Preferably, the formed layer is anoxide layer, which can be used as a dielectric layer. Examples of suchlayers include barium tantalates, barium niobates, strontium tantalates,strontium niobates, magnesium tantalates, magnesium niobates, calciumtantalates, calcium niobates, barium tantalate titanates, barium niobatetitanates, strontium tantalate titanates, strontium niobate titanates,magnesium tantalate titanates, magnesium niobate titanates, calciumtantalate titanates, calcium niobate titanates, barium-strontiumtantalates, barium-strontium niobates, barium-strontium tantalatetitanates, barium-strontium niobate titanates, magnesium-strontiumtantalates, magnesium-strontium niobates, calcium-strontium tantalatetitanates, calcium-strontium niobate titanates, and combinationsthereof.

In one embodiment, the present invention provides a method of forming alayer on a substrate, such as is used in the manufacturing of asemiconductor structure. The method includes: providing (preferably in adeposition chamber) a substrate (preferably a semiconductor substrate orsubstrate assembly such as a silicon wafer); providing a vapor includingone or more Group IIA metal precursor compounds of the formula M(NRR′)₂,wherein R and R′ are each independently an organic group (preferablyhaving 1 to 10 carbon atoms, which are optionally replaced by orsubstituted with silicon, oxygen, and/or nitrogen atoms and/or groupscontaining such atoms), and M is selected from the group consisting ofbarium, strontium, calcium, and magnesium (preferably, strontium andbarium); providing a vapor comprising one or more Group VB metalprecursor compounds (preferably tantalum and/or niobium precursorcompounds); and directing the vapors to and/or contacting the vaporswith the substrate to form a metal-containing layer (preferably, a metaloxide layer, which is useful as a dielectric layer) on one or moresurfaces of the substrate using a vapor deposition process (e.g., achemical vapor deposition process or an atomic layer deposition processthat includes a plurality of deposition cycles). Optionally, the methodfurther includes providing one or more reaction gases (preferably, watervapor) and directing the gases to or contacting the gases with thesubstrate.

Optionally, the methods of the present invention can further include astep of providing a vapor including one or more metal-containingprecursor compounds other than the compounds of Formula I and other thanthe one or more Group VB metal precursor compounds, and directing thisvapor to the substrate to form a metal-containing layer. Such compoundsare preferably titanium compounds, such as those of the formula Ti(AR¹_(x))₄, wherein: A is O, N, C(O), or OC(O); and R¹ is a (C1-C10)alkylgroup, wherein two of the R¹ alkyl groups are optionally joined togetherto form an alkylene group; and n=1 or 2. Using such additional precursorcompounds, mixed-metal oxides can be formed such as barium tantalatetitanates, barium niobate titanates, strontium tantalate titanates,strontium niobate titanates, magnesium tantalate titanates, magnesiumniobate titanates, calcium tantalate titanates, calcium niobatetitanates, barium-strontium tantalate titanates, barium-strontiumniobate titanates, calcium-strontium tantalate titanates,calcium-strontium niobate titanates, and combinations thereof.

The precursor compounds can be directed to the substrate together (e.g.,substantially simultaneously) or separately. They can be directed to thesubstrate in the same cycle or in separate (e.g., alternating) cycles.Some or all of the precursor compounds can be directed to the substratebefore directing one or more reaction gases to the substrate.

In another embodiment, the present invention provides a method ofmanufacturing a memory device structure. The method includes: providinga substrate (preferably a semiconductor substrate or substrate assemblysuch as a silicon wafer) having a first electrode thereon; providing oneor more Group IIA metal precursor compounds of the formula M(NRR′)₂,wherein R and R′ are each independently an organic group and M isselected from the group consisting of barium, strontium, calcium, andmagnesium; providing one or more Group VB metal precursor compounds(preferably tantalum and/or niobium precursor compounds); vaporizing theprecursor compounds; contacting the vaporized precursor compounds andthe one or more reaction gases with the substrate using a vapordeposition process to form a dielectric layer on the first electrode ofthe substrate; and forming a second electrode on the dielectric layer.

In yet another embodiment, the present invention provides a vapordeposition system (preferably an atomic layer deposition system), thatincludes: a deposition chamber optionally having a substrate (preferablya semiconductor substrate or substrate assembly such as a silicon wafer)positioned therein; one or more vessels that include one or more GroupIIA metal precursor compounds of the formula M(NRR′)₂, wherein R and R′are each independently an organic group and M is selected from the groupconsisting of barium, strontium, calcium, and magnesium; and one or morevessels that include one or more Group VB metal precursor compounds(preferably tantalum and/or niobium precursor compounds).

“Substrate” as used herein refers to any base material or constructionupon which a metal-containing layer can be deposited. The term“substrate” is meant to include semiconductor substrates and alsoinclude non-semiconductor substrates such as films, molded articles,fibers, wires, glass, ceramics, machined metal parts, etc.

“Semiconductor substrate” or “substrate assembly” as used herein refersto a semiconductor substrate such as a metal electrode, basesemiconductor layer or a semiconductor substrate having one or morelayers, structures, or regions formed thereon. A base semiconductorlayer is typically the lowest layer of silicon material on a wafer or asilicon layer deposited on another material, such as silicon onsapphire. When reference is made to a substrate assembly, variousprocess steps may have been previously used to form or define regions,junctions, various structures or features, and openings such ascapacitor plates or barriers for capacitors.

“Layer” as used herein refers to any metal-containing layer that can beformed on a substrate from the precursor compounds of this inventionusing a vapor deposition process. The term “layer” is meant to includelayers specific to the semiconductor industry, such as “barrier layer,”“dielectric layer,” and “conductive layer.” (The term “layer” issynonymous with the term “film” frequently used in the semiconductorindustry.) The term “layer” is also meant to include layers found intechnology outside of semiconductor technology, such as coatings onglass.

“Dielectric layer” as used herein is a term used in the semiconductorindustry that refers to an insulating layer (sometimes referred to as a“film”) having a high dielectric constant that is typically positionedbetween two conductive electrodes to form a capacitor. For thisinvention, the dielectric layer contains a Group IIA metal and a GroupVB metal, where preferably the compound is a tantalate and/or niobate,and optionally a titanate.

“Precursor compound” as used herein refers to a metal compound capableof forming (typically in the presence of a reaction gas) ametal-containing layer on a substrate in a vapor deposition process. Theresulting metal-containing layers are typically oxide layers, which areuseful as dielectric layers.

“Deposition process” and “vapor deposition process” as used herein referto a process in which a metal-containing layer is formed on one or moresurfaces of a substrate (e.g., a doped polysilicon wafer) from vaporizedprecursor compound(s). Specifically, one or more metal precursorcompounds are vaporized and directed to one or more surfaces of a heatedsubstrate (e.g., semiconductor substrate or substrate assembly) placedin a deposition chamber. These precursor compounds form (e.g., byreacting or decomposing) a non-volatile, thin, uniform, metal-containinglayer on the surface(s) of the substrate. For the purposes of thisinvention, the term “vapor deposition process” is meant to include bothchemical vapor deposition processes (including pulsed chemical vapordeposition processes) and atomic layer deposition processes.

“Chemical vapor deposition” (CVD) as used herein refers to a vapordeposition process wherein the desired layer is deposited on thesubstrate from vaporized metal precursor compounds and any reactiongases used within a deposition chamber with no effort made to separatethe reaction components. In contrast to a “simple” CVD process thatinvolves the substantial simultaneous use of the precursor compounds andany reaction gases, “pulsed” CVD alternately pulses these materials intothe deposition chamber, but does not rigorously avoid intermixing of theprecursor and reaction gas streams, as is typically done in atomic layerdeposition or ALD (discussed in greater detail below). Also, for pulsedCVD, the deposition thickness is dependent on the exposure time, asopposed to ALD, which is self-limiting (discussed in greater detailbelow).

“Atomic layer deposition” (ALD) as used herein refers to a vapordeposition process in which numerous consecutive deposition cycles areconducted in a deposition chamber. Typically, during each cycle themetal precursor is chemisorbed to the substrate surface; excessprecursor is purged out; a subsequent precursor and/or reaction gas isintroduced to react with the chemisorbed layer; and excess reaction gas(if used) and by-products are removed. As compared to the one cyclechemical vapor deposition (CVD) process, the longer duration multi-cycleALD process allows for improved control of layer thickness byself-limiting layer growth and minimizing detrimental gas phasereactions by separation of the reaction components. The term “atomiclayer deposition” as used herein is also meant to include the relatedterms “atomic layer epitaxy” (ALE) (see U.S. Pat. No. 5,256,244(Ackerman)), molecular beam epitaxy (MBE), gas source MBE,organometallic MBE, and chemical beam epitaxy when performed withalternating pulses of precursor compound(s), reaction gas and purge(i.e., inert carrier) gas.

“Chemisorption” as used herein refers to the chemical adsorption ofvaporized reactive precursor compounds on the surface of a substrate.The adsorbed species are irreversibly bound to the substrate surface asa result of relatively strong binding forces characterized by highadsorption energies (>30 kcal/mol), comparable in strength to ordinarychemical bonds. The chemisorbed species are limited to the formation ofa monolayer on the substrate surface. (See “The Condensed ChemicalDictionary”, 10th edition, revised by G. G. Hawley, published by VanNostrand Reinhold Co., New York, 225 (1981)). The technique of ALD isbased on the principle of the formation of a saturated monolayer ofreactive precursor molecules by chemisorption. In ALD one or moreappropriate reactive precursor compounds are alternately introduced(e.g., pulsed) into a deposition chamber and chemisorbed onto thesurfaces of a substrate. Each sequential introduction of a reactiveprecursor compound is typically separated by an inert carrier gas purge.Each precursor compound co-reaction adds a new atomic layer topreviously deposited layers to form a cumulative solid layer. The cycleis repeated, typically for several hundred times, to gradually form thedesired layer thickness. It should be understood, however, that ALD canuse one precursor compound and one reaction gas.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an exemplary capacitor construction.

FIG. 2 is a perspective view of a vapor deposition coating systemsuitable for use in the method of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention provides methods of forming a metal-containinglayer on a substrate using one or more Group IIA metal precursorcompounds of the formula M(NRR′)₂ (Formula I), wherein: R and R′ areeach independently an organic group; and M is selected from the groupconsisting of barium, strontium, calcium, and magnesium (preferably, Mis Ba or Sr); and one or more Group VB metal precursor compounds. Othermetal-containing precursor compounds (other than those of Formula I andother than the one or more Group VB metal precursor compounds) can alsobe used as can one or more reaction gases in the methods of the presentinvention.

The metal-containing layer formed is a Group IIA metal-containing layer,preferably a strontium- and/or barium-containing layer. In addition, theGroup IIA metal-containing layers include a Group VB metal. The layersor films formed can be in the form of Group IIA metal oxide-containingfilms, for example, wherein the layers include one or more Group IIAmetal oxides doped with one or more Group VB metals, and optionallyother metals. Thus, the term “Group IIA metal oxide” films or layersencompass doped films or layers (i.e., mixed metal oxides), such ascalcium, barium, strontium, and/or magnesium, tantalates and/orniobates, and optionally titanates.

The substrate on which the metal-containing layer is formed ispreferably a semiconductor substrate or substrate assembly. Any suitablesemiconductor material is contemplated, such as for example,conductively doped polysilicon (for this invention simply referred to as“silicon”). A substrate assembly may also contain a layer that includesplatinum, iridium, rhodium, ruthenium, ruthenium oxide, titaniumnitride, tantalum nitride, tantalum-silicon-nitride, silicon dioxide,aluminum, gallium arsenide, glass, etc., and other existing orto-be-developed materials used in semiconductor constructions, such asdynamic random access memory (DRAM) devices and ferroelectric memory(FERAM) devices, for example.

Substrates other than semiconductor substrates or substrate assembliescan be used in methods of the present invention. These include, forexample, fibers, wires, etc. If the substrate is a semiconductorsubstrate or substrate assembly, the layers can be formed directly onthe lowest semiconductor surface of the substrate, or they can be formedon any of a variety of the layers (i.e., surfaces) as in a patternedwafer, for example.

The Group IIA metal precursor compounds useful in this invention are ofthe formula M(NRR′)₂ (Formula I) wherein R and R′ are each independentlyan organic group. As used herein, the term “organic group” is used forthe purpose of this invention to mean a hydrocarbon group that isclassified as an aliphatic group, cyclic group, or combination ofaliphatic and cyclic groups (e.g., alkaryl and aralkyl groups). In thecontext of the present invention, suitable organic groups for precursorcompounds of this invention are those that do not interfere with theformation of a metal-containing layer using vapor deposition techniques.In the context of the present invention, the term “aliphatic group”means a saturated or unsaturated linear or branched hydrocarbon group.This term is used to encompass alkyl, alkenyl, and alkynyl groups, forexample. The term “alkyl group” means a saturated linear or branchedmonovalent hydrocarbon group including, for example, methyl, ethyl,n-propyl, isopropyl, t-butyl, amyl, heptyl, 2-ethylhexyl, and the like.The term “alkenyl group” means an unsaturated, linear or branchedmonovalent hydrocarbon group with one or more olefinically unsaturatedgroups (i.e., carbon-carbon double bonds), such as a vinyl group. Theterm “alkynyl group” means an unsaturated, linear or branched monovalenthydrocarbon group with one or more carbon-carbon triple bonds. The term“cyclic group” means a closed ring hydrocarbon group that is classifiedas an alicyclic group, aromatic group, or heterocyclic group. The term“alicyclic group” means a cyclic hydrocarbon group having propertiesresembling those of aliphatic groups. The term “aromatic group” or “arylgroup” means a mono- or polynuclear aromatic hydrocarbon group. The term“heterocyclic group” means a closed ring hydrocarbon in which one ormore of the atoms in the ring is an element other than carbon (e.g.,nitrogen, oxygen, sulfur, etc.).

As a means of simplifying the discussion and the recitation of certaintemninology used throughout this application, the terms “group” and“moiety” are used to differentiate between chemical species that allowfor substitution or that may be substituted and those that do not soallow for substitution or may not be so substituted. Thus, when the term“group” is used to describe a chemical substituent, the describedchemical material includes the unsubstituted group and that group forexample, substituted with silicon atoms or donor atoms such asnonperoxidic oxygen (e.g., in the chain (i.e., ether) as well ascarbonyl groups or other conventional substituents), nitrogen or sulfur.Where the term “moiety” is used to describe a chemical compound orsubstituent, only an unsubstituted chemical material is intended to beincluded. For example, the phrase “alkyl group” is intended to includenot only pure open chain saturated hydrocarbon alkyl substituents, suchas methyl, ethyl, propyl, t-butyl, and the like, but also alkylsubstituents bearing further substituents known in the art, such ashydroxy, alkoxy, alkylsulfonyl, halogen atoms, cyano, nitro, amino,carboxyl, etc. Thus, “alkyl group” includes ether groups, haloalkyls,nitroalkyls, carboxyalkyls, hydroxyalkyls, sulfoalkyls, etc. On theother hand, the phrase “alkyl moiety” is limited to the inclusion ofonly pure open chain saturated hydrocarbon alkyl substituents, such asmethyl, ethyl, propyl, t-butyl, and the like.

Preferably, the Group IIA metal precursor compounds useful in thisinvention are of the formula M(NRR′)₂ wherein: R and R′ are eachindependently an organic group, preferably having from 1 to 10 carbonatoms, which are optionally replaced by or substituted with silicon,oxygen, and/or nitrogen atoms or groups containing such atoms; and M isselected from the group consisting of strontium, barium, calcium, andmagnesium (more preferably, strontium and barium). More preferably, theGroup IIA metal precursor compounds are of the formula M[N(SiR″₃)₂]₂,wherein M is selected from the group consisting of barium and strontium,and R″ is a (C1-C3)alkyl moiety.

Examples of useful such precursors compounds include Ba[N(SiMe₃)₂],₂and/or Sr[N(SiMe₃)₂]₂, where Me is methyl. During the use of suchcompounds, hexamethyl disilazane (HMDS) is the single volatileby-product during the vapor deposition process. This makes the processvery compatible with conventional semiconductor fabrication processes.Such compounds are described in Vaartstra et al., Inorg. Chem.,30:121-125(1991), for use in CVD processes; however, there was noindication that such compounds could be used in ALD processes.

Such compounds can be made using conventional techniques. For example,Ba[N(SiMe₃)₂]₂ can be prepared as described by Vaartstra et al. inInorg. Chem., 30:121-125(1991), “Syntheses Synthesis and Structures of aSeries of Very Low Coordinate Barium Compounds: Ba[N(SiMe₃)₂]₂(THF)₂,{Ba[N(SiMe₃)₂](THF)₂}, and {Ba[N(SiMe₃)₂]₂}₂,” by reacting in a dryboxbarium granules with HN(SiMe₃)₂ (available from Aldrich Chemical Co.Milwaukee, Wis.) in the presence of gaseous ammonia and tetrahydrofuran.Also, Sr[N(SiMe₃)₂]₂can be prepared using essentially the same syntheticprocedure but replacing the barium granules with an equimolar quantityof strontium granules. Another synthetic approach involves the reactionof a Group IIA metal halide and Li[N(SiMe₃)₂].

A wide variety of Group VB metal precursor compounds are known in theart and can be used in the present invention. Preferably, the Group VBmetal precursor compounds are tantalum precursor compounds, niobiumprecursor compounds, or combinations thereof.

Examples of useful tantalum precursor compounds include, but are notlimited to, tantalum halides (e.g., TaF₅, TaCl₅, and TaBr₅), tantalumalkoxides (e.g., Ta(OCH₃)₅, Ta(OC₂H₅)₅, Ta(OC₄H₉)₅,Ta(OC₂H₅)₄(OCH₂CH₂O-iso-C₃H₇), and Ta(OCH₃)₄(OCH₂CH₂O-iso-C₃H₇)),tantalum amides (e.g., pentakis(dimethylamino)tantalum), tantalumimido-amides (e.g., tris(diethylamino)(ethylimino)tantalum andtris(diethylamino)(tert-butylimino)tantalum), tantalum carboxylates,tantalum alkyls, tantalum hydrides, and combinations thereof.

Examples of useful niobium precursor compounds include, but are notlimited to, niobium halides (e.g., NbF₅, NbCl₅, and NbBr₅), niobiumalkoxides (e.g., Nb(OC₂H₅)₄(CH₃OCH₂CH₂O) and Nb(OC₂H₅)₄((CH₃)₂NCH₂CH₂O),also known as niobium tetraethoxy dimethylaminoethoxide or NbTDMAE),niobium amides (e.g., pentakis(ethylmethylamino)niobium), niobiumcarboxylates, niobium alkyls, niobium hydrides, and combinationsthereof.

Other metal-containing precursor compounds can be used to make variousmixed-metal complexes. For example, titanium precursor compoundssuitable for use in this invention include organo-titanium compoundshaving the formula Ti(AR¹ _(x))₄, wherein: A is a difunctional (x=1) ortrifunctional (x=2) polar group such as —O—, —N<, —C(O)— or —OC(O)—; andR¹ is a (C1-C10)alkyl group, wherein two of the R¹ alkyl groups areoptionally joined together to form an alkylene group. Preferably, A is—O— and R′ is methyl, ethyl, n-propyl, isopropyl, or butyl.

Examples of suitable titanium precursor compounds include titaniumtetramethoxide, titanium tetraethoxide, titanium tetra-n-propoxide,titanium tetraisopropoxide, titanium tetra-n-butoxide, titaniumtetra-t-butoxide, titanium tetra-2-ethylhexoxide,tetrakis(2-ethylhexane-1,3-diolato) titanium (i.e., octyleneglycoltitanate), titanium diisopropoxide bis(acetylacetonate), titaniumdiisopropoxide bis(2,2,6,6-tetramethyl-3,5-heptanedionate, titaniumbis(ethyl acetacetato)diisopropoxide, bis(ethylacetoacetato)bis(alkanolato)titanium, tetrakis(dimethylamino)titanium,tetrakis(diethylamino)titanium, tetrakis(ethylmethylamino)titanium, andtitanium (triethanolaminato)isopropoxide, all available fromSigma-Aldrich Chemical Co., Milwaukee, Wis. or as TYZOR organictitanates from E. I. du Pont de Nemours & Co., Wilmington, Del.Preferably, the titanium precursor compound is a tetralkylorthotitanateof the formula Ti(OR²)₄, wherein all of the R² groups are the same andare (C1-C10)alkyl moieties, preferably (C1-C4)alkyl moieties, e.g.,methyl, ethyl, isopropyl and t-butyl.

The titanium precursor compounds can also be prepared by reacting onemole of titanium tetrachloride with four moles of the organic compound(e.g., an alcohol) needed to provide the desired R² groups. For example,titanium tetraisopropoxide (i.e., tetraisopropylorthotitanate) can beprepared by reacting titanium tetrachloride with isopropyl alcoholfollowed by distillation of the crude reaction product.

The precursor compounds may be liquids or solids at room temperature(preferably, they are liquids at the vaporization temperature).Typically, they are liquids sufficiently volatile to be employed usingknown vapor deposition techniques. However, as solids they may also besufficiently volatile that they can be vaporized or sublimed from thesolid state using known vapor deposition techniques.

Various combinations of reaction gases can also be used in the methodsof the present invention. The reaction gas can be selected from a widevariety of gases reactive with the precursor compounds described herein,at least at a surface under the conditions of atomic layer adsorption.Examples of suitable reaction gases include oxidizing and reducing gasessuch as water vapor, oxygen, ozone, hydrogen peroxide, nitrous oxide,ammonia, organic amines, silanes, hydrogen, hydrogen sulfide, hydrogenselenide, hydrogen telluride, and combinations thereof. Water vapor isthe preferred reaction gas for the deposition of oxides using theprecursor compounds described herein.

The precursor compounds can be vaporized in the presence of an inertcarrier gas if desired. Additionally, an inert carrier gas can be usedin purging steps, as described below. The inert carrier gas is typicallyselected from the group consisting of nitrogen, helium, argon, andmixtures thereof. In the context of the present invention, an inertcarrier gas is one that is generally unreactive with the complexesdescribed herein and does not interfere with the formation of thedesired metal-containing film (i.e., layer).

The deposition process for this invention is a vapor deposition process.Vapor deposition processes are generally favored in the semiconductorindustry due to the process capability to quickly provide highlyconformal layers even within deep contacts and other openings. Chemicalvapor deposition (CVD) and atomic layer deposition (ALD) are two vapordeposition processes often employed to form thin, continuous, uniform,metal-containing (preferably dielectric) layers onto semiconductorsubstrates. Using either vapor deposition process, typically one or moreprecursor compounds are vaporized in a deposition chamber and optionallycombined with one or more reaction gases to form a metal-containinglayer onto a substrate. It will be readily apparent to one skilled inthe art that the vapor deposition process may be enhanced by employingvarious related techniques such as plasma assistance, photo assistance,laser assistance, as well as other techniques.

The final layer (which is preferably a dielectric layer) formedpreferably has a thickness in the range of about 10 Å to about 500 Å.More preferably, the thickness is in the range of about 50 Å to about200 Å.

Preferably, the vapor deposition process employed in the methods of thepresent invention is a multi-cycle ALD process. Such a process isadvantageous (particularly over a CVD process) in that it provides foroptimum control of atomic-level thickness and uniformity to thedeposited layer (e.g., dielectric layer) and to expose the metalprecursor compounds to lower volatilization and reaction temperatures tominimize degradation. Typically, in an ALD process, each reactant ispulsed sequentially onto a suitable substrate, typically at depositiontemperatures of about 25° C. to about 400° C. (preferably about 100° C.to about 300° C.), which is generally lower than presently used in CVDprocesses. Under such conditions the film growth is typicallyself-limiting (i.e., when the reactive sites on a surface are used up inan ALD process, the deposition generally stops), insuring not onlyexcellent conformality but also good large area uniformity plus simpleand accurate thickness control. Due to alternate dosing of the precursorcompounds and/or reaction gases, detrimental vapor-phase reactions areinherently eliminated, in contrast to the CVD process that is carriedout by continuous coreaction of the precursors and/or reaction gases.(See Vehkamäki et al, “Growth of SrTiO₃ and BaTiO₃ Thin Films by AtomicLayer Deposition,” Electrochemical and Solid-State Letters,2(10):504-506 (1999)).

A typical ALD process includes exposing an initial substrate to a firstchemical species (e.g., a Group IIA or a Group VB metal precursorcompound) to accomplish chemisorption of the species onto the substrate.Theoretically, the chemisorption forms a monolayer that is uniformly oneatom or molecule thick on the entire exposed initial substrate. In otherwords, a saturated monolayer. Practically, chemisorption might not occuron all portions of the substrate. Nevertheless, such an imperfectmonolayer is still a monolayer in the context of the present invention.In many applications, merely a substantially saturated monolayer may besuitable. A substantially saturated monolayer is one that will stillyield a deposited layer exhibiting the quality and/or properties desiredfor such layer.

The first species is purged from over the substrate and a secondchemical species (e.g., a different compound of Formula I, a differentGroup VB metal precursor compound, a metal-containing compound of aformula other than that of Formula I and other than the Group VB metalprecursor compound, or a reaction gas) is provided to react with thefirst monolayer of the first species. The second species is then purgedand the steps are repeated with exposure of the second species monolayerto the first species. In some cases, the two monolayers may be of thesame species. As an option, the second species can react with the firstspecies, but not chemisorb additional material thereto. That is, thesecond species can cleave some portion of the chemisorbed first species,altering such monolayer without forming another monolayer thereon. Also,a third species or more may be successively chemisorbed (or reacted) andpurged just as described for the first and second species.

Purging may involve a variety of techniques including, but not limitedto, contacting the substrate and/or monolayer with a carrier gas and/orlowering pressure to below the deposition pressure to reduce theconcentration of a species contacting the substrate and/or chemisorbedspecies. Examples of carrier gases include N₂, Ar, He, etc. Purging mayinstead include contacting the substrate and/or monolayer with anysubstance that allows chemisorption by-products to desorb and reducesthe concentration of a contacting species preparatory to introducinganother species. The contacting species may be reduced to some suitableconcentration or partial pressure known to those skilled in the artbased on the specifications for the product of a particular depositionprocess.

ALD is often described as a self-limiting process, in that a finitenumber of sites exist on a substrate to which the first species may formchemical bonds. The second species might only bond to the first speciesand thus may also be self-limiting. Once all of the finite number ofsites on a substrate are bonded with a first species, the first specieswill often not bond to other of the first species already bonded withthe substrate. However, process conditions can be varied in ALD topromote such bonding and render ALD not self-limiting. Accordingly, ALDmay also encompass a species forming other than one monolayer at a timeby stacking of a species, forming a layer more than one atom or moleculethick.

The described method indicates the “substantial absence” of the secondprecursor (i.e., second species) during chemisorption of the firstprecursor since insignificant amounts of the second precursor might bepresent. According to the knowledge and the preferences of those withordinary skill in the art, a determination can be made as to thetolerable amount of second precursor and process conditions selected toachieve the substantial absence of the second precursor.

Thus, during the ALD process, numerous consecutive deposition cycles areconducted in the deposition chamber, each cycle depositing a very thinmetal-containing layer (usually less than one monolayer such that thegrowth rate on average is from about 0.2 to about 3.0 Angstroms percycle), until a layer of the desired thickness is built up on thesubstrate of interest. The layer deposition is accomplished byalternately introducing (i.e., by pulsing) Group IIA or Group VB metalprecursor compound(s) and reaction compound(s) into the depositionchamber containing a semiconductor substrate, chemisorbing the precursorcompound(s) as a monolayer onto the substrate surfaces, and thenreacting the chemisorbed precursor compound(s) with the otherco-reactive precursor compound(s). The pulse duration of precursorcompound(s) and inert carrier gas(es) is sufficient to saturate thesubstrate surface. Typically, the pulse duration is from about 0.1 toabout 60 seconds, preferably from about 0.2 to about 30 seconds.

In comparison to the predominantly thermally driven CVD, ALD ispredominantly chemically driven. Accordingly, ALD is often conducted atmuch lower temperatures than CVD. During the ALD process, the substratetemperature is maintained at a temperature sufficiently low to maintainintact bonds between the chemisorbed precursor compound(s) and theunderlying substrate surface and to prevent decomposition of theprecursor compound(s). The temperature is also sufficiently high toavoid condensation of the precursor compounds(s). Typically thesubstrate temperature is kept within the range of about 25° C. to about400° C. (preferably about 150° C. to about 300° C.), which is generallylower than presently used in CVD processes. Thus, the first species orprecursor compound is chemisorbed at this temperature. Surface reactionof the second species or precursor compound can occur at substantiallythe same temperature as chemisorption of the first precursor or, lesspreferably, at a substantially different temperature. Clearly, somesmall variation in temperature, as judged by those of ordinary skill,can occur but still be a substantially same temperature by providing areaction rate statistically the same as would occur at the temperatureof the first precursor chemisorption. Chemisorption and subsequentreactions could instead occur at exactly the same temperature.

For a typical ALD process, the pressure inside the deposition chamber iskept at about 10⁻⁴ torr to about 1 torr, preferably about 10⁻⁴ torr toabout 0.1 torr. Typically, the deposition chamber is purged with aninert carrier gas after the vaporized precursor compound(s) have beenintroduced into the chamber and/or reacted for each cycle. The inertcarrier gas(es) can also be introduced with the vaporized precursorcompound(s) during each cycle.

The reactivity of a precursor compound can significantly influence theprocess parameters in ALD. Under typical CVD process conditions, ahighly reactive compound may react in the gas phase generatingparticulates, depositing prematurely on undesired surfaces, producingpoor films, and/or yielding poor step coverage or otherwise yieldingnon-uniform deposition. For at least such reason, a highly reactivecompound might be considered not suitable for CVD. However, somecompounds not suitable for CVD are superior ALD precursors. For example,if the first precursor is gas phase reactive with the second precursor,such a combination of compounds might not be suitable for CVD, althoughthey could be used in ALD. In the CVD context, concern might also existregarding sticking coefficients and surface mobility, as known to thoseskilled in the art, when using highly gas-phase reactive precursors,however, little or no such concern would exist in the ALD context.

As stated above, the use of the complexes and methods of forming filmsof the present invention are beneficial for a wide variety of thin filmapplications in semiconductor structures, particularly those using highdielectric materials or ferroelectric materials. For example, suchapplications include capacitors such as planar cells, trench cells(e.g., double sidewall trench capacitors), stacked cells (e.g., crown,V-cell, delta cell, multi-fingered, or cylindrical container stackedcapacitors), as well as field effect transistor devices.

A specific example of where a dielectric layer is formed according tothe present invention is a capacitor construction. An exemplarycapacitor construction is a dynamic random access memory device, whichis described with reference to FIG. 1. Referring to FIG. 1, such amemory cell 10 includes a high dielectric material 12, prepared using anALD process to react and deposit the combination of one or more GroupIIA metal precursor compounds of this invention, one or more Group VBmetal precursor compounds, one or more titanium precursor compounds, andwater vapor, for example, between two electrodes 14 and 16, typicallymade of platinum, iridium, ruthenium, ruthenium oxide, or rhodium. Thebottom electrode 16 is typically in contact with a silicon-containinglayer 18, such as an n-type or p-type doped silicon substrate. Aconductive layer 20 is positioned between the bottom electrode 16 andthe silicon-containing layer 18 to act as a barrier layer to diffusionof atoms such as silicon into the electrode and dielectric material.

A system that can be used to perform an atomic layer vapor depositionprocess of the present invention is shown in FIG. 2. The system includesan enclosed vapor deposition chamber 110, in which a vacuum may becreated using turbo pump 112 and backing pump 114. One or moresubstrates 116 (e.g., semiconductor substrates or substrate assemblies)are positioned in chamber 110. A constant nominal temperature isestablished for substrate 116, which can vary depending on the processused. Substrate 116 may be heated, for example, by an electricalresistance heater 118 on which substrate 116 is mounted. Other knownmethods of heating the substrate may also be utilized.

In this process, precursor compounds 160 (e.g., Group IIA metalprecursor compound and/or Group VB metal precursor compounds) are storedin vessels 162. The precursor compounds are vaporized and separately fedalong lines 164 and 166 to the deposition chamber 110 using, forexample, an inert carrier gas 168. A reaction gas 170 may be suppliedalong line 172 as needed. Also, a purge gas 174, which is often the sameas the inert carrier gas 168, may be supplied along line 176 as needed.As shown, a series of valves 180-185 are opened and closed as required.

The following examples are offered to further illustrate the variousspecific and preferred embodiments and techniques. It should beunderstood, however, that many variations and modifications may be madewhile remaining within the scope of the present invention, so the scopeof the invention is not intended to be limited by the examples.

EXAMPLES Example 1 Atomic Layer Deposition of SrTa₂O₆

Separate reservoirs of the compounds Sr[N(SiMe₃)₂]₂ and tantalumpentafluoride are attached to a vapor deposition chamber and heated to130° C. and 75° C., respectively. Lines and valves connecting thereservoirs to the chamber are maintained 20° C. above the reservoirtemperature. The Sr[N(SiMe₃)₂]₂ remains solid; subliming into the vaporphase. The tantalum source melts at 97° C., but has sufficient vaporpressure at 75° C. The substrate is a silicon wafer which has beenprocessed up to the bottom electrode of the capacitor. The substrate ison a heated stage held at 300° C. The chamber is pumped down to a basepressure of 10⁻⁵ torr before the ALD cycles are initiated and remainsunder dynamic vacuum for the duration of the deposition. The precursorsare pulsed into the chamber using pneumatic actuated valves undercomputer control. A Sr-source pulse of 10 seconds is followed by a1-second purge gas pulse of argon followed by a 30-second pump-downunder vacuum. A 1-second water vapor pulse is then introduced from awater reservoir held at ambient temperature and the vapor controlled at25 sccm through a mass flow controller. The water pulse is followed by a1-second argon purge (controlled at 50 sccm), and then a 30-secondpump-down. A Ta-source pulse is then introduced for 5 seconds followedby a 1-second argon purge followed by a 30-sec pump-down. Another watervapor pulse step the same as previous ends the complete cycle. Thissequence is repeated for 300 cycles, yielding a SrTa₂O₆ film that ispreferably approximately 250 Angstroms thick.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

What is claimed is:
 1. A method of forming a mixed metal oxide,comprising: providing a semiconductor substrate or substrate assembly;providing a first vapor comprising a first precursor having the formulaM₁(NRR′)₂, wherein R and R′ are each independently an organic group andM₁ is selected from the group consisting of barium, strontium, calcium,and magnesium; providing a second vapor comprising a second precursorthat includes tantalum or niobium; providing a third vapor comprising athird precursor comprising oxygen; and directing the first, second andthird vapors to the semiconductor substrate or substrate assembly toform an oxide comprising M₁ M₂O using a vapor deposition process.
 2. Themethod of claim 1 wherein the oxide has the formula SrTa₂O₆.
 3. Themethod of claim 1 wherein the vapor deposition process is an atomiclayer deposition process.
 4. The method of claim 1 wherein the vapordeposition process is a chemical vapor deposition process.
 5. The methodof claim 1 wherein the second precursor is selected from the groupconsisting of metal halides, metal alkoxides, metal amides, metalimido-amides, metal carboxylates, metal alkyls and metal hydrides.
 6. Amethod of mixed metal composition, the method comprising: providing asemiconductor substrate or substrate assembly; providing a first vaporcomprising a first precursor having the formula M₁(NRR′)₂, wherein R andR′ are each independently an organic group and M₁ is selected from thegroup consisting of barium, strontium, calcium, and magnesium; providinga second vapor comprising a second precursor having the formula M₂X₅;where M₂ is tantalum or niobium, and where X is fluorine, chlorine orbromine; and directing the first and second vapors to the semiconductorsubstrate or substrate assembly to form a metal-containing layer on oneor more surfaces of the semiconductor substrate or substrate assemblyusing a vapor deposition process; the metal layer comprising a mixtureof M₁ and M₂.
 7. The method of claim 6 wherein the second precursor isTaF₅.
 8. The method of claim 7 wherein the first precursor isSr[N(SiMe₃)₂]₂.
 9. The method of claim 6 wherein the vapor depositionprocess is an atomic layer deposition process.
 10. The method of claim 6wherein the vapor deposition process is a chemical vapor depositionprocess.
 11. A method of forming a mixed metal oxide, comprising:providing a semiconductor wafer in a reaction chamber; flowing a firstvapor into the chamber, the first vapor comprising a first precursorhaving the formula Sr[N(SiMe₃)₂]₂; flowing a second vapor into thechamber, the second vapor comprising a second precursor having theformula TaF₅; flowing a third vapor into the chamber, the third vaporcomprising water; and the first, second and third vapors being in thechamber at substantially non-overlapping times relative to one anotherto form the mixed metal oxide SrTa₂O₆ over the semiconductor wafer.